There are known two types of capacitive tough sensing technologies: self-capacitance touch sensing and mutual capacitance touch sensing. In both technologies, touch sensing involves charging and discharging a sensor capacitor having a capacitance which varies depending on touching, by applying a given sensing wave signal; receiving a response signal from the sensor capacitor generated in response to the sensing wave signal; and measuring the magnitude of the response signal. In connection with this, techniques have been variously proposed for improving the sensitivity of touch sensing.
For example, Japanese Patent Application Publication No. 2014-106864 A discloses a touch sensing circuit adapted to mutual capacitance touch sensing. In this technique, a rectangular wave signal is used as the sensing wave signal. This technique improves the touch sensing sensitivity by integrating the response signal corresponding to the rising edges of the sensing wave signal and the response signal corresponding to the falling edges with the polarities inverted from each other.
However, there is room for improving the S/N (signal to noise) ratio of the response signal.